Just a few questions about the Autonomic Nervous System. Hopefully they Help!
1. If hexamethonium blocks all
nicotinic acetylcholine receptors, wouldnt all of these functions cease? Don't
all preganglionic synapses release Ach, and all postganglionic receptors are
nicotinic?
Please help clarify why
B is correct.
3. If at rest parasympathetic activity dominates
autonomic outflow. Therefore, the
intravenous infusion of hexamethonium, which causes the block of nicotinic acetylcholine
receptors (nAChR), will cause all of the following will occur except
which?
A.
Heart rate will increase
B.
Blood pressure will decrease
C.
Airways will dilate
D.
Digestion rate will decrease
This is a GREAT question and one that many people struggle with. This has to do with precisely the fact that the parasympathetic is ON at rest, therefore since the entire system is a balance of the two systems, if you turn both off the one that was on will appear to be actually off and the one that was off will appear to be on, therefore the sympathetic activities will appear to increase while the parasympathetic activities will appear to decrease.
2. On the chart you
provided us for the autonomic nervous system target organs, it states that the
sympathetic system uses muscarinic 3 receptors to increase sweating. How is
this so if muscarinic receptors are specifically for cholinergic
neurotransmitters in the parasympathetic nervous system? Is this an exception?
This IS the exception. Remember that ONE Of the sympathetic neurotransmitters that is released is actually cholinergic, and THIS is that one.
3. I had another question for you but i had completely forgotten about it. on the
table found in slide 27. do we need to memorize every single receptor type for
the different organs? or just the main idea?
I wish I could tell you that you do not need to memorize it, but unfortunately this is one of those things you actually will need to know in the long run and I am expecting you to remember now.
4. I have questions
regarding epinephine and nonepinephrine
-Which of the two is
more predominantly secreted?
-For each of them, which
of them are primiarly signaled to? and also in terms of Alpha, beta 1, beta 2
receptors?
At most of the sympathetic post-ganglionic neurons, norepinephrine is released predominantly (~80%) while epinephrine is only released by approximately 20%. However, from the adrenal medulla, epinephrine is the predominant neurontransmitter released (~80%) while norepinephrine is released in much smaller quantities at only approximately 20%.
The specific affinity for the adrenergic receptors for these two neurotransmitters is above the scope of what you need to know for this lecture. Dr. Meisenberg may go into it in more details in the GPCR lecture, but probably will not. Knowing that they both activate adrenergic receptors is sufficient for our purposes.
5. When I was answering
this following question, I was uncertain to answer choice A or D. but the
answer was choice D. Could you explain to me the reason why choice D is
correct?
4. While walking home from Tulips you come across a large
boa constrictor thereby most likely activating one branch of your autonomic
nervous system. The post-ganglionic neurons of this branch of the
autonomic nervous system primarily release what neurotransmitter?
A. Epinephrine
B. Acetylcholine
C. Serotonin
D. Norepinephrine
E. Dopamine
This question can hopefully now be answered with the information given above. The primary neurontrasmitter released from the post-ganglionic neurons of the sympathetic (the fight or flight system) is norepinephrine so is a better answer than A, whereas if the question referred to the adrenal medulla, then A would be a better answer than D.
Hello Dr. J,
ReplyDeleteOn slide 21 of the ANS lecture in the notes it states that the sympathetic post ganglionic nerve are myelinated and then later on in the lecture on slide 25 it says the post ganglionic nerve is unmyelinated. Which one of these is correct?
ssapra,
DeleteThis can be a little confusing, but if you read closely you will note that the slide indicates that there are four distinctly separate neurons here, listed below:
1. Preganglionic Sympathetic (short fibers) = myelinated
2. Postganglionic Sympathetic (long fibers) = unmyelinated
3. Preganglionic Parasympathetic (long fibers) = myelinated
4. Postganglionic Parasympathetic (short fibers) = unmyelinated
Sorry for that typo Ssapra, I apologize for that confusion! What Gary has presented above is indeed correct, not my typo on slide 25.
Deletessapra,
ReplyDeleteBelow you will find a link to an image that will make it visually clear:
http://antranik.org/wp-content/uploads/2011/11/comparison-of-autonomic-and-somatic-motor-systems-cell-bodies-axons-effect-neurotransmittor-ach-ne.jpg
I presume that when we talk about myelination of neurons later on that it will become clear as to why some neurons are myelinated and some are not. Keep in mind that myelination increases the velocity of a nerve impulse. Some nerve impulses to be as fast as possible, such as those going to skeletal muscle. This explains why there is only one neuron and it's myelination. Where as other nerve impulses don't need to be as fast, such as those innervating the digestive track. This explains why there can be more than one neuron and why the whole signal, from the brain to the organ, does't need to be myelinated along the entire track of nerves. Also, very short nerves may not always be myelinated whereas longer one will tend to be. Keeping this in mind may help you rationalize why a nerve may or may not be myelinated.
Thank you Gary for helping with that question. You are EXACTLY right regarding the myelination. I realize there is a typo in the notes section of one of the slides, but indeed the make-up Gary presents is correct. Additionally, the correct answer indicated for the CTL question on this subject is also not correct.
DeleteIt all really is about economy because myelin allows for faster propagation of the action potential, but at the cost of the energy of making myelin, whereas without the myelin, the diameter of the axon needs to be greater in order for accurate propagation of excitable activity, therefore it is a balance of energy and space use.
For question 1, slide 21 in the spinal cord lecture says " At the SYMPATHETIC Nervous system"
ReplyDeletePost-ganglionic nerves release Norepi at the target organs (Ach released in one special tissue)
Also slide 25 mentions this in the footnotes
Is this a question? Yes, the sympathetic releases norepinephrine and ACh in one special case, but ALL of the pre-ganglionic neurons (both sympathetic and parasympathetic) release ACh.
DeleteThanks for doing this blog Dr. J
ReplyDeleteI second the thank you! This blog has been very helpful.
ReplyDeleteI am having a rough time with question 11. Can anyone help me understand why G isn't correct? Are there PANS post-ganglionic neurons that release epinephrine?
As for the second part: ParaSymp post-gang release Ach only SOME sym post-gang release Norepi.
DeleteI'm trying to remember precisely what question 11 is. I presume that it is related to what is released from the sympathetic vs. parasympathetic neurons. Parasympathetic release only ACh while sympathetic neurons release primarily norepinephrine (80%) and 20% epinephrine with one neuron releasing ACh(to sweat glads.
DeleteIf this doesn't clear it up, please remind me what the question is and I would be happy to help :)
11. Which of the following is a feature of the sympathetic, but not the parasympathetic, nervous system?
DeleteA. Ganglia located in the effector organs
B. Long preganglionic neurons
C. Preganglionic neurons release norepinephrine
D. Preganglionic neurons release acetylcholine (ACh)
E. Preganglionic neurons originate in the thoracolumbar spinal cord
F. Postganglionic neurons synapse on effector organs
G. Postganglionic neurons release epinephrine
H. Postganglionic neurons release ACh
The answer is E. Wondering if G is also correct (and if not, why it is considered incorrect). Thanks!
Aaahhh. Well, answer G is technically correct, but it is not the best possible answer choice from those given. E would be a better answer because it is ALWAYS true, whereas G is only true 20% of the time (see above that postganglionic sympathetic neurons release 80% norepinephrine and only 20% epinephrine). Therefore, this is a perfect example of where you need to pick the BEST answer choice and the best answer choice for this question is E, not G.
Delete